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PubMed1992

Reliability of lumbar isometric torque in patients with chronic low back pain.

In this study, the test-retest reliability of lumbar isometric strength testing in patients with chronic low back pain (CLBP) was assessed. Isometric torque measurements were obtained from 89 patients with CLBP at seven different angles of lumbar flexion. Because previous studies have demonstrated significant strength differences between male and female subjects, separate data analyses were performed for each gender. Results indicated moderate to high reliability for patients with CLBP when tested at individually determined angles of flexion within their idiosyncratic range of motion (ROM) (female subjects: r = .59-.96, P less than .05, SEE = 12.0-24.2 N.m; male subjects: r = .71-.93, P less than .05, SEE = 25.1-62.1 N.m). For comparison with previously published data on asymptomatic controls, an additional set of analyses was conducted for subjects with full lumbar ROM. Similar reliability was demonstrated for this subsample (female subjects: r = .57-.93, P less than .05, SEE = 12.4-27.9 N.m; male subjects: r = .63-.93, P less than .05, SEE = 34.2-44.2 N.m). The authors concluded that isometric lumbar extension torque could be reliably measured in patients with CLBP at multiple positions within the full ROM, although reliability decreased at the most extended positions. The demonstrated reliability will allow researchers to assess treatment effects and group differences without undue concern for artifact attributable to measurement error.

Back Pain↗

PubMed1989

Effects of isometric exercise on blood cell adrenoceptors in essential hypertension.

The effect of handgrip (HG) isometric exercise on plasma catecholamines, alpha 2-adrenoceptors on platelets and beta 2-adrenoceptors on lymphocytes was studied in normotensive subjects (NT) and essential hypertensive subjects (HT). Whereas systolic blood pressure (SBP) increases were similar in NT and HT subjects, diastolic blood pressure (DBP) and heart rate (HR) increased more in the former group. Baseline values and changes in plasma epinephrine (E) and norepinephrine (NE) did not differ between both groups. No differences were apparent in alpha 2-adrenoceptor density and affinity between NT and HT subjects before or after the test. HG isometric exercise induced a similar increase in beta 2-adrenoceptors on lymphocytes of 22 +/- 7 and 13 +/- 5% in NT and HT subjects, respectively. Affinity to the beta 2-adrenoceptors under baseline conditions was somewhat lower in HT (8.1 +/- 0.4 pM) than in NT subjects (6.5 +/- 0.5 pM), and this difference persisted during the test. Our results indicate that there are no differences in alpha 2- and beta 2-adrenoceptor densities either at baseline conditions or after HG isometric exercise between NT and HT subjects. Small differences noted in affinity to the beta 2-adrenoceptors require further investigation.

Adult↗

PubMed2000

Generation of reactive oxygen species after exhaustive aerobic and isometric exercise.

UNLABELLED: Many studies have implicated elevated oxygen consumption (VO2) associated with aerobic exercise as contributing to oxidative stress. Only a few studies have investigated nonaerobic exercise and its relation to pro-oxidant and antioxidant activities. PURPOSE: The purpose of this study was to compare biomarkers of oxidative stress: lipid peroxidation, protein oxidation, and total antioxidants in blood after exhaustive aerobic (AE) and nonaerobic isometric exercise (IE). METHODS: Blood samples were collected from 12 subjects who performed a maximum AE and IE test and were analyzed for thiobarbituric acid (TBARS), carbonyls, lipid hydroperoxides (LH), and oxygen radical absorbance capacity (ORAC). RESULTS: VO2 increased 14-fold with AE compared with 2-fold with IE. Protein carbonyls increased 67% (P < 0.05) pre- to immediately and 1 h post-AE, and 12% pre- to immediately post-IE and returned to baseline 1 h post-IE. TBARS did not increase significantly with either treatment. LH increased 36% above rest during IE compared with 24% during AE (P < 0.05). ORAC increased 25% (P < 0.05) pre- to post-AE, compared with 9% (P < 0.05) pre- to post-IE. CONCLUSION: There was evidence of oxidative stress after both exhaustive aerobic and isometric exercise. Lipid hydroperoxides, protein carbonyls, and total antioxidants increased after both IE and AE. Due to the different metabolic demands of aerobic and isometric exercise, we can rule out a mass action effect of VO2 as the sole mechanism for exercise-induced oxidative stress.

Adult↗

PubMed2002

Chronic exertional compartment syndrome: muscle changes with isometric exercise.

UNLABELLED: Chronic exertional compartment syndrome (CECS) is a well-documented cause of lower leg pain in active individuals. The pathophysiology is unclear, although it is generally believed to be associated with increased intramuscular pressure, but there is very little information about muscle function in relation to the onset of pain. PURPOSE: To investigate strength, fatigue, and recovery of the anterior tibial muscles in CECS patients and healthy subjects during an isometric exercise protocol. METHODS: Twenty patients and 22 control subjects (mean age 27.6 yr and 33.0 yr, respectively) performed a 20-min isometric exercise protocol consisting of intermittent maximal voluntary contractions (MVC). Central fatigue was evaluated by comparing changes in electrically stimulated (2 s at 50 Hz) and voluntary contraction force before and during the exercise, and then throughout 10 min of recovery. Muscle size was measured by ultrasonography. Pain and cardiovascular parameters were also examined. RESULTS: The absolute MVC forces were similar, but MVC:body mass of the patients was lower (P < 0.05) as was the ratio of MVC to muscle cross-sectional area (P < 0.01). The extent of central and peripheral fatigue was similar in the two groups. The patients reported significantly higher levels of pain during exercise (P < 0.05 at 4 min) and after the first minute of recovery (P < 0.001). An 8% increase in muscle size after exercise was observed for both groups. There were no differences in the cardiovascular responses of the two groups. CONCLUSIONS: CECS patients were somewhat weaker than normal but fatigued at a similar rate during isometric exercise. Patients reported higher pain than controls despite comparable changes in muscle size, suggesting that abnormally tight fascia are not the main cause of CECS symptoms.

Adult↗

PubMed1993

Trunk strength and lumbar paraspinal muscle activity during isometric exercise in chronic low-back pain patients and controls.

The purpose of this study was to describe trunk strength and lumbar paraspinal muscle activity across five angles of flexion during isometric exercise and rest in chronic low-back pain patients and control subjects. High muscle tension as measured by surface integrated electromyography is predicted by a muscle spasm model, and low muscle tension is predicted by a muscle deficiency model. Prior lumbar surgery had no affect on peak torque or maximum surface integrated electromyography data. Both groups produced greater torque and less surface integrated electromyography in more flexed positions. Chronic low-back pain patients exhibited lower peak torque and lower maximum surface integrated electromyography bilaterally during isometric extension effort across all angles. A muscle deficiency model of chronic low back pain was supported by these data and a muscle spasm model was not supported. Discriminant analyses indicated that monitoring maximum surface integrated electromyography of lumbar muscles during isometric effort facilitates classification of chronic low-back pain patients. Future directions are discussed in terms of applying psychophysiologic methods to pain rehabilitation.

Adult↗

PubMed1996

The nasal response to isometric exercise in non-eosinophilic intrinsic rhinitis.

The exact pathophysiology of intrinsic rhinitis is not fully understood. The generally held belief is that it is due to an imbalance between the outflow of the nasal sympathetic and parasympathetic nervous systems, perhaps due to excessive parasympathetic or reduced sympathetic activity. In this study the nasal airway response to a predominantly sympathetic stimulus, isometric exercise, was studied in 19 patients with intrinsic rhinitis and compared with 16 normal patients. Isometric exercise took the form of a handgrip stimulus using a hand dynomometer. Following sustained handgrip, a small fall of nasal resistance in the normal group (0.058 kPas/1) and a moderate rise in nasal resistance in the rhinitis group (0.242 kPas/1) was found. Pulse and blood pressure changes were the same in both groups with a significant rise in pulse rate and diastolic blood pressure. The study shows that there is an abnormal response to isometric exercise in intrinsic rhinitis, perhaps due to relative nasal sympathetic hyposensitivity.

Airway Resistance↗

PubMed1994

Prediction of pregnancy-induced hypertension by isometric exercise.

The purpose of this study is to evaluate an isometric exercise (Hand-Grip test) as a method to predict pregnancy-induced hypertension (PIH). One hundred and twenty-five pregnant women were given the Hand-Grip (HG) test before the 15th gestational week. The Hand-Grip test was rated positive when the systolic blood pressure increased 15 mmHg or more during isometric exercise or decreased 14 mmHg or more immediately after isometric exercise. As a result, the Hand-Grip test had the highest sensitivity (81.8%) and specificity (68.4%) for predicting PIH, compared to other risk factors. The positive predictive value was 20% (second highest among risk factors, the actual incidence of hypertension was 8.8%), and the negative predictive value was 97.5% (highest). In conclusion, by use of a very simple Hand-Grip test early in gestation, we are able to predict PIH with the highest sensitivity.

Adult↗

PubMed1977

Lactate in fast and slow twitch skeletal muscle fibres of man during isometric contraction.

Concentration of lactate in fast and slow twitch fibres, respectively, were determined in m. quadriceps femoris after sustained contractions at 25%, 50%, and 75% of maximal voluntary isometric contraction (MVC) until exhaustion as well as after interrupted exercises at 25% and 50% MVC. Maximal lactate concentrations were only found at 50% of MVC performed to exhaustion. Lactate concentration was higher in slow twitch (ST) fibres at 50% MVC compared to in ST fibres at 25% MVC, and higher in fast twitch (FT) fibres at 50% MVC compared to in FT fibres at 75% MVC. After short time isometric exercise (i.e. 75% to exhaustion and 50% and 25% performed for the same period of time as 75% MVC) lactate concentration, expressed as lactate ratio (lactate concentration in FT fibres/lactate concentration in ST fibres) was found to be positively correlated to percent FT fibres (r=0.89). Lactate ratio ranged 0.5-2.0, i.e. at onset of isometric exercise, lactate concentration increase was faster in ST fibres in the muscle rich in ST fibres and faster in FT fibres when the muscle wasrich in FT fibres.

Age Factors↗

PubMed1996

The relationship between the intracellular Ca2+ transient and the isometric twitch force in frog muscle fibres.

The calcium-sensitive fluorescent indicator fluo-3 was used to monitor the intracellular free calcium concentration ([Ca2+]i) during isometric twitches in twenty-nine single muscle fibres from the anterior tibialis muscle of Rana temporaria (sarcomere length, 2.2 microns; 2-4 degrees C). The transient change in [Ca2+]i in response to a single stimulus was very brief. The time to peak and the duration of the Ca2+ signal, measured at 50% of the peak amplitude, were 8.3 +/- 0.2 and 22.1 +/- 1.4 ms (mean +/- S.E.M., n = 29), respectively. The mean peak amplitude of the Ca2+ transient was 3.2 +/- 0.1 microM, ranging from 2.46 to 3.92 microM among the different fibres. The isometric force started to rise 2.5 ms before [Ca2+]i reached its maximum value. When peak twitch force was attained, [Ca2+]i had already declined to approximately 10% of its maximum value. The peak force produced during a twitch was closely related to the decay phase of the Ca2+ transient, a slower decay of [Ca2+]i being associated with a greater amplitude of the twitch. The amplitude and duration of the Ca2+ transient varied in a systematic way relative to one another in different fibres, in that a greater amplitude was associated with a more rapid decay of the Ca2+ transient. NO3- and Zn2+ added to the external medium greatly enhanced the peak twitch force without markedly affecting the amplitude of the Ca2+ transient. However, both agents delayed the decay of [Ca2+]i. It is concluded that the decay phase of the Ca2+ transient is a more important determinant of the mechanical response during an isometric twitch than is the peak amplitude of the transient.

Aniline Compounds↗

PubMed1972

Cardiovascular and respiratory responses to changes in central command during isometric exercise at constant muscle tension.

1. Experiments were designed to show whether elements of the command descending from higher centres to exercising muscles provide an input for cardiovascular and respiratory control. Vibration, known to be a powerful stimulus to the primary afferents from muscle spindles, was applied to the biceps tendon of human subjects performing sustained isometric contractions with the biceps or the triceps muscle. When the biceps was contracting this activation of muscle spindle primary afferents in it provided an element of reflex excitation, so that less central command was required to achieve a given tension. When triceps was contracting, the activation of muscle spindle primary afferents in its antagonist, biceps, contributed an element of reflex inhibition, so that more central command than normally was required to achieve a given tension. The cardiovascular and respiratory responses to an isometric effort could thus be investigated at any tension when the central command was normal, decreased, or increased.2. Blood pressure, heart rate, and pulmonary ventilation all increase in an isometric effort. The increase in each is less when the central command is reduced. The increase in each is greater when the central command is increased.3. It is concluded that there is irradiation of cardiovascular and respiratory control centres by the descending central command during voluntary muscular contractions in man.

Adult↗

PubMed2006

Non-invasive vascular impedance measures demonstrate ocular vasoconstriction during isometric exercise.

AIMS: The calculation of impedance for a vascular network is a common method used in circulation studies. Impedance indices (the ratios of the harmonics of pressure to the harmonics of flow) provide the investigator with a measure of the opposition to blood flow in a pulsatile system and are a proven indicator for vasculopathy. Previous studies investigating the eye's opposition to blood flow have concentrated on simple measures of resistance (the ratio of mean pressure difference to mean flow) which are more appropriate to a steady state or non-pulsatile system. The purpose of this study is to demonstrate a new, non-invasive, method to determine the vascular impedance of the eye during the known physiologic stress of sustained isometric exercise. METHODS: Waveforms of ocular blood flow and carotid arterial blood pressure were measured non-invasively. Ocular blood flow waveforms were calculated using the Langham-Silver method by measuring the small fluctuations in intraocular pressure intraocular pressure over time with a high fidelity pneumatonometer. Carotid arterial blood pressure waveforms were determined using a SphygmoCor electronic tonometer held over the common carotid artery of the neck. Both waveforms were recorded simultaneously in normal volunteers under two conditions: (1) a baseline resting state and (2) during sustained isometric exercise. The components of the two waveforms (the harmonics) were calculated using a Fast Fourier transform and expressed as a ratio in order to determine a set of impedance values for each condition. The first four impedance values were calculated. RESULTS: 12 volunteers (six male: six female) with a mean age of 27 years (range 22-32 years) were recruited to the study. In comparison to baseline resting conditions, mean carotid blood pressure and heart rate both increased significantly during exercise: baseline mean carotid blood pressure, 82.6+/-8.2 mm Hg vs exercise mean carotid blood pressure, 93.8+/-12.8 mm Hg (p<0.001); baseline pulse rate, 64.6+/-9.1 BP(m) vs exercise pulse rate, 71.8+/-9.7 BP(m) (p<0.001). Compared to resting conditions, the first and third impedance values demonstrated significant change during exercise: the first impedance value rose (83.9+/-25.6 mm Hg-s/microl to 117.1 +/- 40.9 mm Hg-s/microl, p = 0.01) and the third impedance value fell (487.9 +/- 294.7 mm Hg-s/microl to 248.3+/-206.8 mm Hg-s/microl, p = 0.01). CONCLUSIONS: The present study demonstrates, for the first time, a practical non-invasive method of calculating an index of impedance moduli for the pulsatile quotient of blood flow to the eye. Furthermore, during controlled isometric exercise, the impedance moduli displayed changes consistent with that known for a vascular system during vasoconstriction. The calculation of impedance moduli for the eye therefore shows promise for future investigations into ocular conditions where vascular obstruction is an aetiological factor.

Adult↗

PubMed1994

Training in élite young athletes (the Training of Young Athletes (TOYA) Study): injuries, flexibility and isometric strength.

Using a mixed longitudinal design, the incidence of injuries, and the development of flexibility and isometric strength of the upper and lower limbs were studied for 2 years in 453 élite young athletes (aged between 9 and 18 years) practising football, gymnastics, swimming or tennis. The children suffered from a low incidence of injuries. Strength and flexibility did not exert a significant role in determining injuries. The rate of injury was not significantly different between the 2 years of the study. Young swimmers showed a greater generalized flexibility. Girls were more flexible than boys between the ages of 13 to 16 years. Athletic children are able to exert greater isometric strength than normal schoolchildren. Boys diverged from the normal population at 14 years, while athletic girls were stronger at all ages. Girls were stronger than boys up to age 12, who were still increasing their muscle strength at 19 years. The average maximal isometric strength exerted in both upper and lower limbs in the four sports was not significantly different. Male gymnasts over 11 years old were significantly stronger than all other athletes.

Adolescent↗

PubMed1975

Myocardial lactate metabolism during isometric hand grip test. Comparison with pacing tachycardia.

Twenty-five patients with chest pain were studied by left ventriculography and coronary arteriography. Myocardial metabolic studies were done during control state, pacing tachycardia, isometric hand grip at 30 per cent of maximum force, and combined hand grip plus pacing tachycardia. Nine patients had myocardial lactate abnormality (group 1) as evidenced by myocardial lactate production or decreased extraction (less than 10%). Though tension time index and triple product (left ventricular ejection time times HR times systolic pressure) as determinants of myocardial oxygen consumption were highest during combined hand grip plus pacing tachycardia, myocardial lactate abnormalities were most frequent during pacing tachycardia. The present study indicates that isometric hand grip even if performed during pacing tachycardia is not a sensitive test for detection of myocardial lactate abnormalities. The rising level of arterial lactate during isometric hand grip is the most likely mechanism of positive myocardial arteriovenous lactate difference.

Blood Pressure↗

PubMed1975

Effects of sustained isometric handgrip on praecordial accelerocardiogram in normal subjects and in patients with heart disease.

The effects of isometric exercise on the maximum amplitude of the praecordial accelerocardiogram (as represented by the DE deflection) have been compared in 6 normal subjects (group 1), 12 patients with aortic stenosis (group 2), and 16 patients with myocardial disease (group 3). Whereas the tachycardia and pressor effects of isometric exercise were identical in all three groups, the normal subjects showed a significant decrease in DE during handgrip of 10 +/- 4 per cent (P less than 0.05) as compared with the insignificant increases of 8.5 +/- 6 per cent (P greater than 0.5), and 4 +/- 3.5 per cent (P greater 0.3) observed in the patients in groups 2 and 3. This response in the normal subjects differed significantly from the responses observed in the patients in groups 2 (P less than 0.02) and 3 (P less than 0.01). Of the patients in each of groups 2 and 3, 50 per cent responded abnormally to handgrip in that they showed a significant increase in DE. In the patients with aortic stenosis this subgroup of patients differed from the remainder in that they had a higher resting cardiac index (P less than 0.05). In the patients with myocardial disease this subgroup was characterized by a significantly lower resting left ventricular end-diastolic pressure (P less than 0.02). It seems, therefore, that those patients who increase DE in response to handgrip tend to have better left ventricular function at rest than those who do not. We suggest that this may be because of increased beta adrenergic activity at rest and during isometric exercise in the subgroup who respond to handgrip with an increase in DE.

Adult↗

PubMed1977

Isometric and isotonic contractions in airway smooth muscle.

Canine tracheal smooth muscle was used as an in vitro model of smooth muscle in intrapulmonary airways to determine whether active tension curves derived from isometric and isotonic muscles are similar, and thus resemble striated muscle in this respect. Isometric, isotonic after-loaded, and isotonic free-loaded contractions elicited at different lengths and loads, were analysed. The data demonstrate that length-tension (L-T) diagrams were different in these various types of contractions for electrically and carbachol driven tracheal smooth muscles strips. In general, at any given length active tension is less in isotonic and free-loaded modes of contraction as compared with isometric. We conclude that the ability to actively develop tension at a given length in airway smooth muscle depends on the mode of contraction.

Animals↗

PubMed2005

Liquid crystal helical ribbons as isometric textures.

Deformations that conserve the parallelism and the distances--between layers, in smectic phases; between columns, in columnar phases--are commonplace in liquid crystals. The resulting isometric deformed textures display specific geometric features. The corresponding order parameter singularities extend over rather large, macroscopic, distances, e.g., cofocal conics in smectics. This well-known picture is modified when, superimposed to the 1D or 2D periodicities, the structure is helical. However isometry can be preserved. This paper discusses the case of a medium whose structure is made of 1D modulated layers (a lamello-columnar phase), assuming that the modulations rotate helically from one layer to the next. The price to pay is that any isometric texture is necessarily frustrated; it consists of layers folded into a set of parallel helicoids, in the manner of a screw dislocation (of macroscopic Burgers vector), the modulations being along the helices, i.e. double-twisted. The singularity set is made of two helical disclination lines. We complete this geometric analysis by a crude calculation of the energy of a helical ribbon. It is suggested that the helical ribbons observed in the B7 phase of banana-like molecules are such isometric textures. As a side result, let us mention that the description of double-twist, traditionally made in terms of a partition of the director field into nested cylinders, could more than often be profitably tested against a partition into nested helicoids.

Biopolymers↗

PubMed1979

Myocardial energetics during isometric twitch contractions of cat papillary muscle.

During myocardial tetanus, when activation is maximum and constant, there is a linear relationship throughout contraction between oxygen consumption (MVo2) and the cumulative product of active tension and time (integral of AT). The goal of this study was to determine the relation of MVo2 to integral of AT during isometric myocardial twitch contractions. Ten right ventricular cat papillary muscles were studied in a flow respirometer. MVo2 was determined during contractions unloaded from Lmax to a slack length at successive 100-ms intervals after stimulation. In contrast to the linear relationship observed during tetanus, MVo2/integral of AT varied during twitch contractions: when the muscles were made slack 100 ms after stimulation MVo2/integral of AT was 389 +/- 51 (SE) (nl of O2/mg of dry muscle)/(N of active tension/mm2.s of active tension). This value was 94 +/- 7 at peak active tension and was constant thereafter. There was a continuous increase in cumulative MVo2 as integral of AT increased; before integral of AT began, MVo2 was 0.41 +/- 0.04 (nl of O2/mg)/contraction at Lmax and 0.22 +/- 0.04 at a slack length; at peak isometric tension MVo2 was 1.84 +/- 0.19; for a complete contraction MVo2 was 2.89 +/- 0.25. These data support two concepts 1) activation energy is small and dependent on initial length and tension; and 2) integral of AT is variably energy dependent throughout the entire isometric twitch contraction.

Animals↗

PubMed1994

Evaluation of spontaneous baroreflex modulation of sinus node during isometric exercise in healthy humans.

The purpose of this study was to 1) evaluate the baroreflex (BR) modulation of the sinus node during isometric exercise in humans by analyzing the variations in pulse interval (PI) in response to beat-by-beat spontaneous changes in systolic arterial pressure (SAP), thus avoiding external intervention to alter arterial pressure (AP); and to 2) evaluate the specific influence of muscle chemoreflex on the SAP-PI relationship. Sixteen healthy males were studied during rest, handgrip at 30% of maximum voluntary contraction [isometric handgrip (IHG)], post-IHG arrested forearm circulation (AFC), and recovery. AP and PI were measured continuously and noninvasively. A BR response was defined by series of at least three consecutive beats in which SAP and PI of the following beat either increased or decreased in a linear fashion. In nine subjects, forearm (FVR) and calf vascular resistances (CVR) were determined. Mean slope (by linear regression) of SAP-PI sequences did not significantly differ between rest, IHG, and AFC (14.1 +/- 2.0, 12.2 +/- 1.6, and 13.2 +/- 1.4 ms/mmHg, respectively), i.e., BR sensitivity was unchanged. IHG resulted in a rightward shift of the regression line relating SAP to PI. The shift was maintained during AFC, when PI returned to control and AP fell slightly but remained significantly elevated. CVR, which did not change during IHG, significantly increased during AFC, whereas FVR increased during both IHG and AFC, but not significantly. The data indicate that arterial BR is "reset" to a higher operating point during isometric exercise. Muscle chemoreflex appears to be partially involved in this modification.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗